<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>设置 下边框的宽度</title>
</head>

<style>
    p.one{
    border-style: solid;
    border-width: 5px;   
    }
</style>
    <p>下边框的宽度为5px</p>
</html>